Traditional materials (e.g., metals, plastics, ceramics, resins, concrete, etc.) do not always provide components with all the requisite properties sufficient for adequate performance under field service conditions. Moreover, despite decades of intensive research to provide improved methods and materials, substantial demand still exists in many commercial and industrial applications for improved technology and low-cost methods to improve final component performance (e.g., enhanced strength, enhanced mechanical behavior characteristics, weight reduction, improved wear resistance, enhanced surface activity/reactivity and/or properties, enhanced thermal conductivity, low and/or balanced and/or controlled coefficients of thermal expansion (CTE), reduced residual stress during the forming process and during thermal cycling of reinforced components in service, enhanced recycle potential, reduced fuel consumption, reduced pollutant emissions and green house gases, etc).
Reinforcement of traditional materials. Matrix composites generally refer to traditional materials (material systems) comprising one or more discrete reinforcement constituents (the reinforcement material(s)) distributed within a continuous phase (the matrix material). The distinguishing characteristics of such matrix composites derive from the properties of the reinforcement constituent(s), from the architectural shape and geometry of such constituent(s), and from the properties of the interfaces between and among different constituents and the matrix. In particular applications, prior art forming and manufacturing processes are designed to provide a uniform distribution of the reinforcement constituent in the matrix. In alternate applications, the distribution of the reinforcement constituent is non-uniform. For example, centrifugal casting applications provide for gradient or layered distributions of reinforcement constituent(s), but are impractical as discussed below and are subject to Coriolis effects that preclude uniform concentric particle density at any given radial position. Additionally, applications comprising infiltration casting of matrix materials into porous reinforcement ‘preforms’, while not providing for continuous gradients, nonetheless provide for positioning of reinforcement constituent(s) within a defined portion of a larger casting (i.e., placement of the preform at a defined position within a casting). In both uniform and non-uniform applications, it is important that there is an adequate bond formed between the matrix material and the discrete reinforcing constituent(s), without substantial degradation of the mechanical properties of the reinforcing constituent(s). Particle reinforcement is a preferred reinforcement constituent/material, and typically comprises non-metallic and commonly ceramic particles (e.g., SiC, Al2O3, etc.), but may comprise a variety of particles and materials that provide advantages or reinforcement for one or more properties of the matrix composite. Reinforcement of matrix material with fibers, continuous-fibers, monofilament, and/or short-fibers is also known in the art. Generally, different types of matrix composites require or are preferably associated with different primary processing routes/methods (e.g., in-situ reactive processes, diffusion bonding, blending and consolidation, vapor deposition and consolidation, liquid-state processing, stir casting/slurry casting, centrifugal casting, and infiltration processes involving infiltration of matrix material into porous ‘preforms’).
Deficiencies of the art. Post-manufacture machining of matrix composite materials comprising durable reinforcement can be time-consuming and expensive, and near net-shape forming, and selective reinforcement techniques have therefore been used to help reduce manufacturing costs. For example, in situ selective reinforcement methods involving placement and positioning of a pre-cast reinforcement material member into a near net-shape casting mold, followed by casting of matrix material around the reinforcement member is known in the art. However, while the amount and/or density of pre-cast reinforcement material can be varied as desired, the reinforcement constituent material of the reinforcement members is not integrated (not mixed or infiltrated) with the matrix material, except perhaps in a limited extent at the interfacial boundaries between the reinforcement member and the unreinforced matrix material. Therefore, such in situ methods are hindered by abrupt and problematic differential coefficients of thermal expansion (CTE) between the matrix and reinforcement member. Such abrupt transitions in CTE at the matrix:reinforcement interface boundaries not only give rise to residual stress during the forming process (e.g., residual stress-concentration), but also manifest in stress fractures during thermal cycling of the reinforced components in service.
Likewise, in another example, there are substantial deficiencies in in situ selective reinforcement methods involving infiltration casting of matrix material into porous ‘preforms’ (comprising reinforcement constituent(s)) positioned in near net-shape casting molds. While such prior art ‘preform’ methods are fast, and result in a more integrated, infiltrated reinforcement ‘preform’ with substantially more contact area between the reinforcement and matrix materials, they are still substantially hindered/limited by abrupt transitions in CTE at the interface/boundaries between the ‘preform’ and the unreinforced matrix material that results in stress problems as described above. Additionally, there are practical limits to the amount/density of reinforcement material in the porous ‘preforms,’ because resistance to infiltration casting substantially increases at high reinforcement levels (e.g. beyond 15% to 20% material in the ‘preform’). Furthermore, while ‘preforms’ are typically positioned in casting molds that are preheated to facilitate infiltration, such preheating, for practical reasons, is at a temperature significantly less than the melting temperature of the molten matrix material (e.g., aluminum). Therefore, there are practical limits to the thickness/cross-sectional area of such prior art performs, because the matrix material must completely infiltrate the ‘preform’ prior to significant cooling of the molten matrix material. Because of this, prior art ‘preforms’ are typically not thicker than about 0.400 inches, placing a practical limitation on the extent of reinforcement that can be integrated into the finished casting.
In yet another example, there are substantial deficiencies in selective reinforcement methods involving centrifugal casting (in near net-shape casting molds) of composite material to favorably place or distribute reinforcement particles within a matrix material of differing density (see, e.g., U.S. Pat. No. 5,980,792 to Chamlee). While abrupt transitions in CTE at the matrix:reinforcement interface boundaries can be reduced in those centrifugal embodiments where continuous particle gradients are formed within the matrix material, such methods still suffer from differential CTE effects in cost-effective embodiments comprising layered reinforcement particles. Moreover, all centrifugal casting embodiments (including that of U.S. Pat. No. 5,980,792) are relatively slow (particularly when used with moderate to high reinforcement particle densities) compared to other casting methods (e.g., high pressure die casting, squeeze casting, etc.), and are thus impractical and too expensive for most commercial applications. Additionally, in centrifugal methods, the attainable variations of particle distributions are limited to bands or layers and/or continuous gradients, and if different reinforcement particle types having differing densities are simultaneously used, it may be impossible to get adequate coordinate (co-localized) particle gradient distributions for the divergent particle types, or to get the different particle types where they are needed, and in the desired pattern.
In further examples, there are substantial deficiencies in selective reinforcement methods involving deposition or spraying (e.g., by low or high velocity spray techniques) of reinforcement particles onto the surface of near net-shape matrix material castings. A major limitation of such methods for these applications is that the spray or deposition is superficial, because it is applied to the surface of solid matrix material castings, and does not substantially penetrate beyond the surface. Additionally, such superficial reinforcement coatings must generally be significantly machined prior to placing the reinforced casting into service. Moreover, absent resurfacing with more reinforcement, the effective service life of such castings is over once the superficial reinforcement layer is worn and/or otherwise degraded. Furthermore, in such superficial reinforcement applications, bonding and integration of the sprayed/deposited reinforcement with the matrix material is limited, even with the most optimal spray/deposition methods.
In further examples, there are substantial deficiencies in making functionally gradient materials having preforms made by methods such as gelcasting methods (see, e.g., U.S. Pat. No. 6,375,877 to Lauf et al), where gravitational or centrifugal forces are used to achieve a vertical composition gradient in molded slurries to form gradient preforms, which may be subsequently infiltrated. Like centrifugal casting embodiments (including that of U.S. Pat. No. 5,980,792), such preform gelcasting methods are relatively slow (particularly when used with high reinforcement particle densities), and are thus too expensive and impractical for most commercial applications. Additionally, in such gelcasting gravitational or centrifugal methods, the attainable variations of particle distributions are limited to layers and/or continuous gradients, and if different reinforcement particle types having differing densities are simultaneously desired/used, it may be impossible to get adequate coordinate (co-localized) particle gradient distributions for the divergent particle types, or to get the different particle types where they are needed, and in the desired pattern. Additionally, preforms made by such gelcasting methods are substantially problematic because of excessive warpage and anisotropic shrinkage occurring during the sintering stage because of different sintering kinetics for the material components. This is particularly true of gelcast preforms made from slurries having less than 60% v. % total solids (see, e.g., U.S. Pat. No. 6,375,877 to Lauf et al., at Example 1)
Therefore, there are substantial deficiencies in prior art selective reinforcement composite material applications, including but not limited to impracticality and lack of versatility (e.g., centrifugation methods), differential CTE problems (e.g., in situ reinforcement member casting, in situ reinforcement ‘preform’ castings, layered centrifugation methods), limitations on ‘preform’ thickness/cross-section, superficiality problems (e.g., surface spray/deposition methods), and impracticality and warpage/anisotropric shrinkage problems (gelcasting methods). Moreover, these deficiencies have substantially limited the scope of current casting or forming crafts including, but not limited to: centrifugal casting; high pressure die casting; vacuum die casting; squeeze casting; high vacuum permanent mold casting; low vacuum permanent mold casting; vacuum riserless/pressure riserless casting, surface spray and deposition methods, etc.
There is, therefore, a pronounced need in the art for novel and effective methods and compositions to increase the scope of current selective reinforcement casting or forming crafts by making the methods and compositions more practical (e.g., faster, more cost effective, etc.), more versatile (in terms of the amount, thickness, distribution, pattern and types of reinforcement constituents that can be applied/used), and less susceptible to mechanisms (e.g., differential CTE between materials) that give rise to stress-fracture during formation and/or thermal cycling during service conditions.
There is a pronounced need in the art for more effective methods to produce functional gradient and non-gradient reinforced composite materials with optimum and/or customized properties (e.g., enhanced strength, enhanced mechanical behavior characteristics, weight reduction, improved wear behavior, enhanced surface reactivities and/or properties (e.g., enhanced reactivity between a surface of a composite material and a friction material interacting therewith), enhanced thermal conductivity, low and/or balanced/controlled coefficients of thermal expansion (CTE), reduced residual stress during the forming process and during thermal cycling of reinforced components in service, enhanced recycle potential, reduced fuel consumption, reduced pollutant emissions and green house gases, etc).
There is a pronounced need for cost-effective, high-throughput methods to make variable density preforms, and for novel casting apparatus to make preforms and particularly variable density preforms
There is a pronounced need in the art for novel and improved matrix composites (e.g., lightweight brake drums, disk brake rotors, cylinder liners, etc.) comprising such preforms.